U.S. patent number 10,845,520 [Application Number 15/129,882] was granted by the patent office on 2020-11-24 for optical devices with patterned anisotropy incorporating parallax optic.
This patent grant is currently assigned to ROLIC AG. The grantee listed for this patent is ROLIC AG. Invention is credited to David Pires, Klaus Schmitt, Hubert Seiberle.
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United States Patent |
10,845,520 |
Schmitt , et al. |
November 24, 2020 |
Optical devices with patterned anisotropy incorporating parallax
optic
Abstract
The invention provides a method for generation of an orientation
pattern in a photo-alignable material using parallax optic. The
invention further provides optical devices comprising a parallax
optical element and an element with patterned optical anisotropic
properties. Such devices have angular dependent, optically
anisotropic properties, which are useful for various
applications.
Inventors: |
Schmitt; Klaus (Lorrach,
DE), Seiberle; Hubert (Weil am Rhein, DE),
Pires; David (Allschwil, CH) |
Applicant: |
Name |
City |
State |
Country |
Type |
ROLIC AG |
Zug |
N/A |
CH |
|
|
Assignee: |
ROLIC AG (Zug,
CH)
|
Family
ID: |
1000005202363 |
Appl.
No.: |
15/129,882 |
Filed: |
March 30, 2015 |
PCT
Filed: |
March 30, 2015 |
PCT No.: |
PCT/EP2015/056826 |
371(c)(1),(2),(4) Date: |
September 28, 2016 |
PCT
Pub. No.: |
WO2015/150295 |
PCT
Pub. Date: |
October 08, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170139093 A1 |
May 18, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Apr 3, 2014 [EP] |
|
|
14163316 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
30/25 (20200101); B42D 25/445 (20141001); G02B
5/3083 (20130101); B42D 25/364 (20141001); G02B
5/3016 (20130101); B29D 11/00644 (20130101); G02B
30/27 (20200101); B29K 2995/0044 (20130101); B29K
2105/0058 (20130101) |
Current International
Class: |
G02B
5/30 (20060101); B42D 25/445 (20140101); B42D
25/364 (20140101); G02B 30/27 (20200101); G02B
30/25 (20200101); B29D 11/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
103581643 |
|
Feb 2014 |
|
CN |
|
2 759 855 |
|
Jul 2014 |
|
EP |
|
2 405 543 |
|
Mar 2005 |
|
GB |
|
2001525080 |
|
Dec 2001 |
|
JP |
|
2005-78091 |
|
Mar 2005 |
|
JP |
|
2011176525 |
|
Sep 2011 |
|
JP |
|
2013/042737 |
|
Mar 2013 |
|
WO |
|
Other References
International Search Report for PCT/EP2015/056826 dated Jun. 11,
2015. cited by applicant .
Notification of Reasons for Refusal dated Feb. 5, 2019 from the
Japanese Patent Office in application No. 2016-560560. cited by
applicant.
|
Primary Examiner: Glick; Edward J
Assistant Examiner: Quash; Anthony G
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
The invention claimed is:
1. A method for the generation of an orientation pattern in a
photo-alignment layer, comprising, providing a photo-alignment
layer (1, 31) providing a parallax optical element (3, 23, 32)
arranging the parallax optical element in a proper distance from
the photo-alignment layer irradiation of the parallax optical
element with aligning light (6) of a first polarization direction
(7) under a first incidence angle (8) with regard to a reference
plane of the parallax optical element such that the aligning light
is steered by the parallax optical element to first regions (9, 34)
on the surface of the photo-alignment layer in order to induce
anisotropy in the first regions of the photo-alignment layer
irradiation of the parallax optical element with aligning light
(16) of a second polarization direction (17) under a second
incidence angle (18) with regard to a reference plane of the
parallax optical element, without changing the mutual position and
orientation of photo-alignment layer and parallax optical element,
such that the aligning light falling on the same area of the
parallax optical element as in the irradiation step with aligning
light of the first polarization direction is steered by the
parallax optical element to second regions (11, 36) on the
photo-alignment layer (1, 31) in order to induce anisotropy in the
second regions of the photo-alignment layer, wherein a photo-mask
comprising a pattern is used in the irradiation step with aligning
light of the first polarization direction to locally block aligning
light such that only first zones of the first regions are
irradiated, and wherein the parallax optical element is irradiated
with aligning light under the first incidence angle but with a
second polarization direction with or without a photo-mask, such
that aligning light is steered to second zones within the first
regions on the photo-alignment layer in order to induce anisotropy
in the second zones with a different orientation direction than in
the first zones.
2. The method according to claim 1, wherein the parallax optical
element comprises microlenses, lenticular lenses (33) or a parallax
barrier plate (3, 23).
3. The method according to claim 2, wherein a photo-alignment layer
(1, 31) is combined with the parallax optical element (23, 32).
4. The method according to claim 1, wherein a photo-alignment layer
(1, 31) is combined with the parallax optical element (23, 32).
5. The method according to claim 1, characterized by one or more
additional irradiations steps, in which aligning light of
additional polarization directions is incident under additional
angles in order to generate alignment in additional regions.
6. The method according to claim 1, wherein a second irradiation
step is applied under the second incidence angle of the aligning
light, without changing the mutual position and orientation of
photo-alignment layer and parallax optical element, and wherein the
aligning light has a different polarization direction in the first
and second irradiation step under the second incidence angle.
7. The method according to claim 1, characterized by an irradiation
step, in which aligning light (26) is irradiated to the
photo-alignment layer (1) without passing a parallax optical
element (3, 23, 32), with a polarization direction (27, 30)
different from polarization directions (10, 35, 37) used for
irradiation using a parallax optical element.
8. An optical device (40, 60, 83, 90) comprising a parallax optical
element (42, 62, 92) combined with a photo-alignment layer and an
optical element (41, 61, 91) with patterned optical properties,
wherein the pattern has been generated by a photo-alignment method
in the photo-alignment layer and wherein the pattern comprises at
least one area, in which the optical property is anisotropic and
wherein the parallax optical element is arranged with a proper
distance from the optical element such that there is a first and a
second incident direction such that light incident onto the
parallax optical element from the first incident direction is
steered to first regions of the optical element having a first
optical property and that light incident onto the same area of the
parallax optical element from the second direction is steered to
second regions of the optical element having a second optical
property and wherein at least one optical property of the first
region differs from that of the second region and wherein first and
second regions are not identical.
9. The optical device according to claim 8, wherein the parallax
optical element comprises microlenses, lenticular lenses or a
parallax barrier plate.
10. The optical device according to claim 9, wherein the optical
element with patterned optical properties is a patterned retarder
(91).
11. The optical device according to claim 9, wherein the optical
element with patterned optical properties is a patterned polarizer
(41, 61).
12. The optical device according to claim 8, wherein the optical
element with patterned optical properties is a patterned retarder
(91).
13. The optical device according to claim 8, wherein the optical
element with patterned optical properties is a patterned polarizer
(41, 61).
14. The optical device according claim 8, wherein the optical
element with patterned optical properties comprises a liquid
crystal polymer.
15. The optical device according to claim 14, wherein the liquid
crystal polymer comprises a dichroic and/or a fluorescent dye.
16. A booklet (80) comprising a patterned retarder (81)
representing an image on a first page (82) and a device (83)
according to claim 10 on a second page (84).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a National Stage of International Application
No. PCT/EP2015/056826 filed Mar. 30, 2015, claiming priority based
on European Patent Application No. 14163316.4 filed Apr. 3, 2014,
the contents of all of which are incorporated herein by reference
in their entirety.
TECHNICAL FIELD
The invention relates to a method for generation of an orientation
pattern in a photo-alignable material using parallax optic. The
invention further relates to optical devices with patterned
anisotropic properties and parallax optic. The devices according to
the invention have angular dependent, optically anisotropic
properties, which are useful for various applications.
BACKGROUND OF THE INVENTION
Elements with patterned anisotropic properties are, for example,
known as optical elements, which include a layer comprising
polymerized or cross-linked liquid crystals with locally different
optical axes directions. Such layers are, for example, prepared by
applying cross-linkable liquid crystal materials on top of an
alignment layer exhibiting locally different alignment directions.
The liquid crystal material adopts the local alignment direction of
the underlying alignment layer and is then cross-linked to fix the
orientation.
Optical elements of that kind are produced in large quantities and
are mainly used for polarization conversion in passive 3D-displays
to encode picture information for the left and right eyes of a
viewer.
There are different methods known in the art to generate an
orientation pattern in a layer of a photo-alignable material. In
general, an orientation pattern is achieved by exposing different
regions of a photo-alignment layer to aligning light with different
polarization directions. For example, in U.S. Pat. No. 7,375,888
this is done by covering part of the photo-alignment layer by
different photo-masks in subsequent exposure steps, each using its
own polarization direction.
In U.S. Pat. No. 7,375,888 optical elements with a layer comprising
patterned anisotropy are disclosed, in which at least two images
are stored, such that the images can be seen one after the other by
rotating an analyzer. The images are, for example, contained in
alternate stripes within the layer with patterned anisotropy. The
method for the manufacturing of such elements, as described in U.S.
Pat. No. 7,375,888, comprises subsequent exposure steps with
individual optical masks, which requires exact alignment of the
masks in order to transfer the individual images to the
corresponding dedicated stripes.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a simplified
method for the generation of an orientation pattern in a layer
comprising a photo-alignable material. Another object of the
present invention is to provide novel optical devices comprising
anisotropic properties.
In the method according to the invention parallax optic is used to
direct aligning light to certain regions of a photo-alignment layer
in order to generate anisotropy in the corresponding regions.
Different regions are selected by the angle of incidence of the
aligning light with regard to the parallax optical element.
Aligning light of different incidence angles may be applied in
subsequent exposure steps or simultaneously, for example, by using
non-collimated light. This allows to generate an alignment pattern
in a photo-alignment layer, for example in the form of stripes,
just by irradiation from different angles without replacing or
repositioning of photo-masks.
Parallax optic is well known in the art and is often employed for
steering light into certain viewing areas in order to separate
different view images. Applications are, for example, in
autostereoscopic displays or in flip pictures with interlaced
images, where the different images can be seen by changing the
viewing angle.
In the context of this invention the term parallax optical element
is used for those optical elements, which provide the parallax
optic and have the property to steer light to different regions as
a function of the incidence angle. Examples of parallax optical
elements are parallax barriers, lenticular lens arrays, grating
plates and microlens arrays. In the following the term POE is used
as an abbreviation for a parallax optical element.
Devices according to the invention comprise a POE and an optical
element with patterned optical properties. The pattern comprises at
least one zone, in which the optical property is anisotropic.
However, there may be zones in the pattern without any anisotropic
property. Properties which may be anisotropic include absorption,
scattering, reflection, luminescence and refractive index.
Preferably, there are at least two zones with anisotropic
properties, which differ in the orientation direction of the
symmetry axis of the anisotropic property. For uniaxial anisotropic
properties the symmetry axis is well defined, such as the optical
axis in case of a uniaxial retarder. Another example is the
extinction axis in case of a polarizing layer. In case the
anisotropy is biaxial, such as in a biaxial retarder, the term
symmetry axis shall refer to one of the main axes. The POE and the
optical element are arranged behind each other, such that they at
least partially overlap with each other. The devices of the
invention use parallax optic to select specific regions of the
pattern of the optical element for interaction with incident light.
The light may be incident to the device from the optical element
side or from the POE side.
In the context of this application the term "orientation direction"
shall refer to the symmetry axis of the anisotropic property. The
term "orientation pattern" shall mean a pattern comprising at least
two areas which differ in the orientation direction.
An orientation pattern in an optical element with patterned optical
properties has preferably been generated by a photo-alignment
method in a layer comprising a photo-alignable material.
Alternatively, the orientation pattern may also have been generated
by other suitable methods, for example by imprinting, brushing,
photolithography or other methods for generating an anisotropic
surface structure.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further illustrated by the accompanying drawing
figures. It is emphasized that the various features are not
necessarily drawn to scale.
FIG. 1 depicts steps of a method according to the invention, which
shows the arrangement of a parallax barrier plate and of a
photo-alignment layer in FIG. 1a, a first irradiation from a first
incident direction in FIG. 1b, a second irradiation from a second
incident direction in FIG. 1c as well the generated orientation
pattern in FIG. 1d.
FIG. 2 depicts steps of a variant of the method according to the
invention, which shows in FIG. 2a a parallax barrier element to
which a photo-alignment layer is attached, a first irradiation from
a first incident direction in FIG. 2b, a second irradiation from
the side opposite of the parallax barrier plate in FIG. 2c as well
the generated orientation pattern in FIG. 2d.
FIG. 3 illustrates steps of an example of the method, depicted in
FIGS. 3a to 3e, wherein a photo-alignment layer is combined with a
POE comprising an array of lenticular lenses.
FIG. 4 shows a device according to a first preferred embodiment
wherein the anisotropic optical element is not in the focal plane
of the lenticular lenses of the POE.
FIG. 5 shows a device according to a first preferred embodiment
which works for a broad range of incident angles.
FIG. 6 shows an example, wherein a device according to the first
preferred embodiment is incorporated in a booklet for analysing
hidden information in a patterned retarder arranged on another page
of the booklet.
FIG. 7 shows a device according to a second preferred embodiment,
wherein the optical element is a patterned retarder layer.
DETAILED DESCRIPTION OF THE INVENTION
According to a first aspect of the invention, there is provided a
method for the generation of an orientation pattern in a
photo-alignment layer.
The method of the invention comprises the steps of providing a
photo-alignment layer providing a parallax optical element
arranging the parallax optical element in a proper distance from
the photo-alignment layer irradiation of the parallax optical
element with aligning light of a first polarization direction under
a first incidence angle with regard to a reference plane of the
parallax optical element such that the aligning light is directed
to first regions on the surface of the photo-alignment layer in
order to induce anisotropy in the first regions of the
photo-alignment layer.
In the context of the present application, the term photo-alignment
layer is used for a layer which comprises a photo-alignable and/or
photo-aligned material, no matter if it has already been exposed to
aligning light or not. Accordingly, a photo-alignment layer, as
used herein, may have no anisotropic property as long as it has not
been exposed to aligning light and has anisotropic property after
it has been exposed to aligning light. A photo-alignment layer may
be applied to a substrate as a thin layer. It is also possible that
the photo-alignment layer is thick and mechanically stable enough,
such that it can be handled without an additional support. In the
latter case, the photo-alignment layer has also the function of a
substrate.
A photo-alignable material is a material which is sensitive to the
polarization of light and in which anisotropic properties can be
induced upon exposure to polarized light of a proper wavelength.
The term "photo-aligned material" is used to refer to a
photo-alignable material that has been aligned by exposure to
aligning light.
In the context of the present application, the term "aligning
light" shall mean light, which can induce anisotropy in a
photo-alignable material and which is at least partially linearly
or elliptically polarized. In case the aligning light is
elliptically polarized, the polarization direction shall be the
major axis of the polarization ellipse. Preferably, the aligning
light is linearly polarized with a degree of polarization of more
than 5:1. Wavelengths, intensity and energy of the aligning light
are chosen depending on the photosensitivity of the photo-alignable
material. Typically, the wavelengths are in the UV-A, UV-B and/or
UV-C range or in the visible range. Preferably, the aligning light
comprises light of wavelengths less than 450 nm. More preferred is
that the aligning light comprises light of wavelengths less than
400 nm.
The methods and devices of the present invention make use of a POE.
A first type of suitable POEs includes focusing elements like
lenses and arrays of lenses, in particular microlenses and
lenticular lenses, which focus the transmitted light into certain
regions in the focal plane of the lenses. Upon changing the
incidence angle of the light, the regions to which the light is
projected move correspondingly. The POE may also comprise optically
anisotropic lenses, preferably these are optically anisotropic
lenticular lenses.
Another type of POEs are parallax barrier plates, which comprise a
plurality of light transmitting sections, separated by light
blocking sections. Preferably, the sections have the form of
stripes. If a parallax barrier plate is arranged at a distance from
a screen and is illuminated obliquely, the light transmitting
sections are projected to the screen with a parallax. Because the
parallax depends on the incidence angle of the light, the
illuminated regions on the screen move as a function of the
incidence angle of the light. Typically, the light blocking
sections are arranged on a support and may absorb and/or reflect
the light. For operation in transmission the support has to be
transmissive, whereas this is not required if operated in
reflection. A POE may comprise one or more parallax barrier plates.
If the POE comprises two or more parallax barrier plates, they are
preferably arranged at a distance from each other, such that
incident light which passes the first barrier plate is further
steered into a certain direction because other directions may be
blocked by light blocking section of a second barrier plate. For
example, this allows to increase the collimation degree of the
light. It is, for example, possible to have parallax barrier plates
on both sides of a transparent substrate, but it is also possible
that the parallax barrier plates are physically separated from each
other. Any method known in the art can be used to generate the
light blocking sections, for example by printing or by other
methods for local material deposition. Alternatively, the light
blocking material may first be applied over an area larger than
that desired for the light blocking sections and subsequently be
removed by proper means, such as dry or wet etching, local ablation
or de-metallization. As an alternative, the light transmissive
sections may also be areas in which the material has been removed
in the full depth of a light absorbing or reflecting plate, thereby
creating holes.
In a parallax barrier plate used in the methods and the devices of
the invention, the width of the light transmissive and light
blocking sections may be the same or different from each other. If
only two kinds of regions have to be distinguished in the
photo-alignment layer (method) or the element with patterned
optical property (device), respectively, by different incidence
angles, then the width of the light transmissive and light blocking
sections is preferably identical. If more than two regions are to
be addressed by more than two incidence angles, then the width of
the light blocking sections is preferably broader than that of the
transmissive sections. Preferably, the ratio of the width of a
light blocking section to the sum of the width of a light blocking
and a light transmissive section is 0.6 or higher, more preferred
0.7 or higher and most preferred 0.8 or higher.
In order to provide a sufficient parallax effect in a reasonable
range of incidence angles for the method of the invention, a
parallax plate should have a proper distance from the
photo-alignment layer. The proper distance depends on the width of
the light transmissive and light blocking sections of the parallax
plate. If the space between the parallax plate and the
photo-alignment layer is filled with air, then the distance between
the parallax plate and the photo-alignment layer is preferably
larger than 0.2 times the width of a light transmissive section of
the parallax plate. More preferred is that the distance is larger
than 0.4 times the width of a light transmissive section and most
preferred larger than 0.6 times the width of a light transmissive
section of the parallax plate. If there is a dielectric material
between the parallax plate and the photo-alignment layer, such as
glass or plastic, then the distance between the parallax plate and
the photo-alignment layer is preferably larger than 0.5 times the
width of a light transmissive section of the parallax plate. More
preferred is that the distance is larger than 0.8 times the width
of a light transmissive section and most preferred larger than one
time the width of a light transmissive section of the parallax
plate.
Still another example of a POE comprises a diffractive structure,
such as a grating plate. The diffracted light impinges only into
certain regions of a screen positioned at a distance from the
device. Because light diffraction depends on the incidence angle of
the light, the regions on the screen to which light is diffracted
change their position as a function of the incidence angle of the
light.
Ideally, a POE used in the method and in the devices of the
invention does not affect the polarization state of the aligning
light. Hence, the materials used in the POEs preferably have low or
no optical birefringence.
The photo-alignment layer may be attached to the POE or may be
separated from the POE. In the latter case the photo-alignment
layer and the POE can be moved and positioned independently from
each other. Further, if the photo-alignment layer is separated from
the POE there is the advantage that the POE can be used for the
method of the invention many times.
Preferably, the photo-alignment layer is combined with the POE.
This is particularly advantageous, if the photo-alignment layer
will be used for manufacturing of an element for a device according
to the invention. Because the POE is combined with the
photo-alignment layer, the pattern generated in the photo-alignment
layer by irradiation through the POE is already perfectly aligned
with the POE. The same POE is therefore used in the method for
generating the pattern and in the device for analyzing the
pattern.
When combining the POE and the photo-alignment layer there should
be a proper distance between the optically active part of the POE
and the surface of the photo-alignment layer. For this purpose the
POE may be provided as a device with a thickness such that when the
photo-alignment layer is applied to the desired surface of the POE
device, it has the proper distance from the POE. Alternatively,
additional layers may be applied to the side of the POE to which
the photo-alignment layer is intended to be applied in order to
provide the proper distance. The photo-alignment layer may be
directly created on the POE, for example, by coating or printing.
Alternatively, a substrate with a photo-alignment layer or a
substrate comprising a photo-alignable material may be laminated to
the POE. In case the POE is a microlens array or a lenticular lens
array then for many applications the photo-alignment layer is
preferably positioned in the focal plane of the lens array.
Preferably, the method of the invention comprises an additional
step, in which, without changing the mutual position and
orientation of photo-alignment layer and parallax optical element,
the parallax optical element is irradiated with aligning light
under a second incidence angle with regard to a reference plane of
the parallax optical element such that the aligning light is
directed to second regions on the surface of the photo-alignment
layer, where it creates anisotropy. Additional exposure steps may
be added, in which aligning light is incident under additional
angles in order to generate alignment in additional regions. The
polarization directions of the aligning light may be the same in
each of the exposure steps or they may differ in two or more of the
exposure steps. For each of the above exposures the relative
position and orientation between alignment layer and parallax
optical element is the same.
The first and second incidence angle shall be different from each
other. Accordingly, the first and second regions are not identical.
Although there may be some overlap of the regions, there is at
least part of the second regions, which does not overlap with areas
of the first regions. The total area of the part of the second
regions that overlap with areas of the first regions is preferably
less than 50%, more preferred less than 30% and most preferred less
than 10% of the total area of the second regions.
Preferably, there is one exposure step, in which aligning light is
irradiated to the photo-alignment layer without passing the POE.
The aligning light may be irradiated to the same side of the
photo-alignment layer which is also irradiated through the POE.
Preferably, the aligning light is irradiated to the side of the
photo-alignment layer, which is opposite to that irradiated through
the POE. The aligning light may be irradiated to the full area of
the photo-alignment layer or only to certain zones of it. It is
further possible to add one or more subsequent steps, in which
further zones of the photo-alignment layer are irradiated with
aligning light of different polarization directions. In order to
define the zones to be irradiated in these exposure steps,
photomasks can, for example, be used. Preferably, the polarization
directions of the aligning light used for irradiation without the
POE are different from each of those used for irradiation through
the POE. The exposure steps with and without the POE may be in any
sequence. For example, the first exposure step may be without the
POE, followed by exposure steps with POE. Preferably, there is an
exposure step without a POE after the last exposure step with a
POE.
The drawings of FIGS. 1a to 1d depict an example of a method
according to the invention. In FIG. 1a a parallax barrier plate is
used as a POE 3, which is arranged at a distance from a
photo-alignment layer 1 on a substrate 2. The parallax barrier
plate has stripes of a light blocking material on a transparent
support, which results in light blocking stripes 5 and transparent
stripes 4. In FIG. 1b, collimated aligning light 6 is incident to
the POE under a first incident angle 8, with regard to the normal
of the POE surface. The polarization direction 7 of the aligning
light is assumed to lie in the drawing plane. Because the light is
blocked in the areas 5, the light transmitted through the
transparent sections 4 creates anisotropy with an orientation
direction 10 only in the first regions 9 of the photo-alignment
layer. Although the drawing indicates that the orientation
direction lies in the plane of the drawing, it is appreciated that
it is also possible that the orientation is perpendicular to the
drawing plane, which depends on the type of photo-alignable
material used in the photo-alignment layer. FIG. 1c illustrates a
second irradiation with collimated aligning light 16 with a second
polarization direction 17 incident under a second incidence angle
18. The polarization direction is assumed to be perpendicular to
the drawing plane, as indicated by the circles 17. Because of the
parallax, aligning light transmitted through the transparent
stripes 4 of the POE irradiate second regions 11 and create
anisotropy in the photo-alignment layer 1 with an orientation
direction 12 perpendicular to the orientation direction 10 created
in the first regions 9. As a result, an orientation pattern is
created in the photo-alignment layer 1 having stripes 9 and 11 with
orientation directions 10 and 12, respectively, which are
perpendicular to each other, as shown in FIG. 1d. The two specific
polarization directions of the aligning light in the two
irradiation steps have been chosen for ease of illustration.
However, any other combination of polarization directions may be
chosen, in particular the two polarization directions do not need
to be perpendicular to each other.
The drawings of FIGS. 2a to 2d depict another variant of the method
according to the invention. Contrary to the example in FIG. 1, the
POE 23 comprises a transparent substrate 22 with stripes of a light
blocking material, thereby forming light transmitting sections 4
and light blocking sections 5 in the form of stripes. The
transparent substrate 22 has a thickness that provides the desired
parallax at the side opposite to the barrier pattern (the backside)
for light with a certain incidence angle. Such a POE may, for
example, be a transparent foil to which opaque stripes have been
printed, for example using a dye, in particular a black dye. The
photo-alignment layer 1 is combined with the POE 23. This may be
done by directly generating the photo-alignment layer on the
backside of the substrate 22, for example by a coating or printing
method or by a lamination process. In FIG. 2b, collimated aligning
light 6 is incident to the POE under a first incident angle 8, with
regard to the normal of the POE surface. The polarization direction
7 of the aligning light is assumed to lie in the drawing plane.
Because the light is blocked in the areas 5, the light transmitted
through the transparent sections 4 creates anisotropy with an
orientation direction 10 only in the first regions 9 of the
photo-alignment layer. An additional irradiation step is depicted
in FIG. 2c, in which the aligning light 26 does not pass the POE,
but is irradiated directly to the alignment layer 1 on the backside
of substrate 22. The circles 27 indicate a polarization direction
perpendicular to the drawing plane, but any other polarization
direction is possible. The aligning light 26 creates anisotropy in
regions 11 of the photo-alignment layer 1 with an orientation
direction 12 perpendicular to the already established orientation
direction 10 in the first regions 9. As a result, an orientation
pattern is created in the photo-alignment layer 1 having stripes 9
and 11 with orientation directions 10 and 12, respectively, which
are perpendicular to each other, as shown in FIG. 2d. As in the
example above, the two polarization directions of the aligning
light in the two irradiation steps have been chosen for ease of
illustration. However, any other combination of polarization
directions may be chosen, in particular the two polarization
directions do not need to be perpendicular to each other.
A third example of the method according to the invention is
depicted in FIG. 3. The POE 32 in this example comprises an array
of lenticular lenses 33 as shown in FIG. 3a. For the following
description the term "front side" of the POE shall mean the side of
the POE which exhibits the lenticular lenses, which is the upper
part in FIG. 3a. For the opposite side of the POE 32, which is the
lower part of the POE in FIG. 3a, the term "backside" shall be
used. This terminology is for ease of description only and shall
not imply any limitation to the scope of the invention. FIG. 3a
further shows that the POE is combined with a photo-alignment layer
31. The photo-alignment layer is applied to the backside of the
POE, for example by coating, printing or lamination. The geometry
of the POE is such that upon a first irradiation of the POE with
aligning light 6, which is incident under a first incident angle 8
and which has a first polarization direction 7, the aligning light
is redirected to first regions 34, as depicted in FIG. 3b. The
first polarization direction 7 of the aligning light is assumed to
lie in the drawing plane. The aligning light causes anisotropy in
regions 34 with an orientation direction 35. FIG. 3c illustrates a
second irradiation of the POE with aligning light 16, which is
incident under a second incident angle 18 and which has a second
polarization direction 17. The second polarization direction 17 is
assumed to be perpendicular to the drawing plane, which is
indicated by the circles in FIG. 3c. In accordance with the
geometry of the POE, the aligning light is redirected to second
regions 36 of the photo-alignment layer, where it creates
anisotropy with an orientation direction 37. The example of the
method incorporates a third irradiation step, as illustrated in
FIG. 3d. In the third irradiation step, the aligning light does not
pass the POE but is irradiated to the backside of the POE, where
the photo-alignment layer is attached to. The aligning light 26 may
be incident perpendicular to the alignment layer plane and has a
third polarization direction 30. Upon irradiation, anisotropy is
created in the so far not exposed regions 38, with a third
orientation direction 39. FIG. 3e shows the orientation pattern in
form of stripes that has been created in the photo-alignment layer
31 by the three irradiation steps. There are three types of regions
34, 36, 38 defined by the corresponding orientation direction. The
polarization directions indicated in FIGS. 3b to 3e, have been
chosen as an example only and shall not limit the scope of the
invention. Any other polarization direction would have been
possible in any of the irradiation steps.
According to a first preferred embodiment of the method of the
invention, a mask comprising a pattern of transparent and opaque
areas is used to locally block the aligning light in order to
irradiate only first zones of those regions selected by the
incidence angle of the aligning light in accordance with the
optical function of the POE.
If the mask is positioned in close contact to the photo-alignment
layer and the aligning light has a high degree of collimation, then
pattern structures even in the micrometer range can be ideally
transferred to the photo-alignment layer. However, if pattern
resolution in the micrometer range is not desired, a lower degree
of light collimation and/or a larger distance of the mask from the
photo-alignment layer can still provide sufficient reproduction
quality. For example, it is possible to project the mask pattern to
the plane of the photo-alignment layer even if the mask is
separated from the photo-alignment layer by several centimeters, as
long as the collimation degree is sufficiently high. Hence, there
is some flexibility in the position of the mask with regard to the
POE and the photo-alignment layer. The mask may be positioned
between the POE and the photo-alignment layer, which allows close
contact of the mask to the photo-alignment layer. However, it is
preferred that the mask is positioned on the side of the POE
opposite to the photo-alignment layer. The aligning light then
first passes the mask and then the POE before it hits the
photo-alignment layer.
Preferably, the first preferred embodiment of the method comprises
a second irradiation step, in which the mask is either removed,
shifted or replaced and wherein without changing the mutual
position and orientation of photo-alignment layer and parallax
optical element, the parallax optical element is irradiated with
aligning light of a second polarization direction, still under the
first incidence angle, such that aligning light is directed to
second zones within the first regions on the photo-alignment layer
in order to induce anisotropy in the second zones with a different
orientation direction than in the first zones. Accordingly, an
orientation pattern is generated in the first regions of the
photo-alignment layer. The number of zones with different
orientation directions may be increased by adding third and further
irradiation steps, each with a different polarization direction of
the aligning light and different or shifted mask pattern or even
without a mask.
The method may be further extended by first and optionally second
and further irradiation steps for a second incidence angle of the
aligning light. The first, second and further irradiation steps
follow the description above, which means that the aligning light
has different polarization directions in each of the irradiation
steps. This generates an orientation pattern of the anisotropy axes
within second regions on the photo-alignment layer.
If it is desired to pattern additional regions, then first, second
and optionally further irradiation steps, as described above, may
be applied for third and further incidence angles of the aligning
light without changing the mutual position and orientation of
photo-alignment layer and parallax optical element. The same mask
may be used for irradiation under different incidence angles.
Preferably, there is one exposure step, in which aligning light is
irradiated to the photo-alignment layer without passing the POE.
The aligning light may be irradiated to the same side of the
photo-alignment layer which is also irradiated through the POE.
Preferably, the aligning light is irradiated to the side of the
photo-alignment layer, which is opposite to that irradiated through
the POE. The aligning light may be irradiated to the full area of
the photo-alignment layer or only to certain zones of it. It is
further possible to add one or more subsequent steps, in which
further zones of the photo-alignment layer are irradiated with
aligning light of different polarization directions. In order to
define the zones to be irradiated in these exposure steps,
photomasks can, for example, be used. Preferably, the polarization
directions of the aligning light used for irradiation without the
POE are different from each of those used for irradiation through
the POE. The exposure steps with and without the POE may be in any
sequence. For example, the first exposure step may be without the
POE, followed by exposure steps with POE. Preferably, there is an
exposure step without a POE after the last exposure step with a
POE.
In the simplest case, there is only a first irradiation step with a
POE for each incident angle of the aligning light, which generates
anisotropy in certain zones of the corresponding region. The zones
are defined by the pattern of the photo-mask, which preferably is
different for each irradiation step. An additional irradiation
without a POE and without a mask but with a different polarization
direction of the aligning light than was used for the irradiation
with the POE, generates anisotropy also in those zones of each
region, which were not irradiated in the steps with the POE. As is
known in the art, the anisotropy axis in zones, which are
subsequently exposed to aligning light of two different
polarization directions may substantially maintain the anisotropy
axis direction, which has been established during the first
exposure step, provided that the exposure energies of first and
second exposure step are properly balanced, whereas the optimum
balance may dependent on the nature of the photo-alignable
material. If the same polarization direction of the aligning light
has been applied for each incident angle of irradiation with POE,
this results in an orientation pattern of the anisotropy axes
having two types of zones, which differ by the direction of the
anisotropy axes.
With the method of the first preferred embodiment it is possible to
transfer information in the form of an orientation pattern to
different regions of a photo-alignment layer. Since the different
regions are individually exposed from different incident
directions, the information transferred to the photo-alignment
layer may be different for each incident angle.
With the method of the first preferred embodiment, it is in
particular possible, to fabricate patterned photo-alignment layers
with alternate stripes and different orientation directions, as
those required for elements described in U.S. Pat. No. 7,375,888.
The advantage is that the new method does not require exact
positioning of the masks and, therefore, there is no need for
register marks.
In a second preferred embodiment of the method of the invention,
the aligning light is spatially modulated by an electronic spatial
light modulator such as a transmissive or reflective liquid crystal
display (LCD), a digital mirror device (DMD) or an organic light
emitting device (OLED). The purpose of this embodiment is the same
as in the first preferred embodiment, namely to modulate the
aligning light such that only desired zones of each region are
irradiated by the aligning light. Compared to the mask of the first
preferred embodiment, which can be regarded as a static spatial
light modulator, the electronic spatial light modulator has the
advantage of a much higher flexibility with regard to the
generation of a pattern, which represents information. Therefore,
the use of an electronic spatial light modulator instead of the
mask is in particular useful if devices to be produced each require
individual information, since the light modulation pattern
representing the information can be generated very quickly, without
manufacturing of a mask. Since electronic spatial light modulators
are employed in many products, in particular for projection
applications, an apparatus comprising the light source, the spatial
light modulator and the projection optics in a single housing may
be used for providing the spatially modulated aligning light.
Because the second preferred embodiment of the method is very
similar to the method of the first preferred embodiment, the
details and variants in the description of the first preferred
embodiment apply also to the second preferred embodiment, except
when referring to details of the mask.
Independent from the specific irradiation method, the anisotropy
induced in a photo-alignment layer may further be transferred to a
slave material, which is in contact with the photo-alignment layer.
As a consequence, the slave material also exhibits anisotropic
properties. A slave material may have been mixed with the
photo-alignable material before exposing it to polarized light or
is brought into contact with the surface of the photo-aligned
material. Therefore, each of the above described embodiments of the
method of the invention may be extended by additional steps, in
which a slave material is applied on top of the photo-alignment
layer, including optional heating and curing steps for establishing
the anisotropic properties in the slave material and to initiate
polymerization, for example by exposure to actinic light. The slave
material may be applied by coating and/or printing but does not
have to cover the entire area of the photo-alignment layer.
Depending on the nature of the slave material, it may be helpful to
perform the polymerization under inert atmosphere, such as nitrogen
or vacuum.
If a slave material is included in the photo-alignment layer or
applied on top of it, above methods may further comprise an
additional step of removing non-polymerized materials from the
slave material, for example by evaporation or dissolving in a
solvent, in order to generate microstructures in the remaining
layer. The slave material to be used in such a method may be
designed such that phase separation of polymerized and
non-polymerized material occurs upon initiating polymerization. For
example, the slave material may comprise non-polymerizable liquid
crystals.
In the context of the present application, a "slave material" shall
refer to any material that has the capability to establish
anisotropy upon contact with a photo-aligned material. The nature
of the anisotropy in the photo-aligned material and in the slave
material may be different from each other. For example, the slave
material may exhibit light absorption anisotropy for visible light
and therefore can act as a polarizer, whereas the anisotropy of the
photo-aligned material may only be related to the molecular
orientation. There may be also moieties of the photo-alignable
material, for example in a co-polymer, which are not sensitive to
aligning light, but create anisotropic properties because of
interaction with the photo-sensitive moieties, which undergo a
photo-reaction upon exposure to aligning light. Such a material
exhibits properties of a photo-alignable material and of a slave
material, but shall be included in the meaning of a photo-alignable
material.
The properties that may be anisotropic in a slave material include
the refractive index, absorption, luminescence, scattering and
reflection.
A slave material may comprise polymerizable and/or
non-polymerizable compounds. Within the context of the present
application the terms "polymerizable" and "polymerized" shall
include the meaning of "cross-linkable" and "cross-linked",
respectively. Likewise, "polymerization" shall include the meaning
of "cross-linking".
Preferably, the slave material is a self-organizing material. More
preferred is that the slave material is a liquid crystal material
and in particular preferred is that the slave material is a liquid
crystal polymer material.
A liquid crystal polymer (LCP) material as used within the context
of this application shall mean a liquid crystal material, which
comprises liquid crystal monomers and/or liquid crystal oligomers
and/or liquid crystal polymers and/or cross-linked liquid crystals.
In case the liquid crystal material comprises liquid crystal
monomers, such monomers may be polymerized, typically after
anisotropy has been created in the LCP material due to contact with
a photo-aligned material. Polymerization may be initiated by
thermal treatment or by exposure to actinic light, which preferably
comprises uv-light. A LCP-material may consist of a single type of
liquid crystal compound, but may also be a composition of different
polymerizable and/or non-polymerizable compounds, wherein not all
of the compounds have to be liquid crystal compounds. Further, an
LCP material may contain additives, for example, a photo-initiator,
dichroic dyes or isotropic or anisotropic fluorescent and/or
non-fluorescent dyes.
According to a second aspect of the invention there is provided a
device comprising a POE and an optical element with patterned
optical properties, wherein the pattern comprises at least one
area, in which an optical property is anisotropic.
Preferably, the optical element has been manufactured according to
the method of the invention described above.
Preferably the anisotropic optical property is the refractive
index, the absorption, the luminescence, optical scattering or
reflection. Most preferred, the anisotropic optical property is the
refractive index or the absorption.
The term "information" as used in this application with regard to
the devices shall cover any kind of coded or non-coded information
that can be displayed, for example, in the form of text including
microtext, images, photographs, graphics, logos and one- or
two-dimensional bar codes.
A first preferred embodiment of a device according to the invention
is a polarizing device which polarizes non-polarized incident light
with different polarization directions, depending on the incidence
angle of the light. Any type of POE can be used for such a device.
As an example, FIGS. 4a and b show cross-sections through a device
40 using a POE 42 with an array of lenticular lenses, wherein the
POE 42 is combined with a photo-alignment layer 41a. The device
further comprises a polarizing layer 41 with patterned optical
properties, wherein the pattern has been generated by a
photo-alignment method in the photo-alignment layer 41a and wherein
the pattern comprises at least one area, in which the optical
property is anisotropic, such as different polarizing directions
44, 46 in different regions 43, 45, which are preferably formed as
stripes. There may be regions between regions 43 and 45, which may
have no polarization function or have any polarization direction.
If non-polarized light 47 is incident from a first direction from
the POE side of the device, as illustrated in FIG. 4a, the light is
directed to first regions 43 having a first polarization direction
44, which in FIG. 4a is assumed to lie in the drawing plane. The
light 48 transmitted through these regions is being polarized
according to this direction, which in FIG. 4a means that the
polarization direction 49 is within the drawing plane. On the other
hand, non-polarized light 50, incident from a second direction, as
illustrated in FIG. 4b, is directed to regions 45 having a second
polarization direction 46, which in FIG. 4b is assumed to be
perpendicular to the drawing plane. The light 51 transmitted
through these regions is then being polarized according to this
direction, which in FIG. 4b means that the polarization direction
52 is perpendicular to the drawing plane, as indicated by the
circle 52. The polarizing layer may be any type of polarizer. For
example, it may be based on commercially available sheet
polarizers, which have been processed to form regions of different
polarization directions. This can, for example, be done by cutting
stripes of different polarization directions and assembling them to
form the patterned polarizer. Preferably, however, the polarizing
layer 41 is a LCP layer comprising dichroic dyes, wherein different
regions have been created by a patterned alignment surface, such as
an alignment layer with an orientation pattern or a surface
treated, for example, by imprinting, brushing, photolithography or
other suitable methods to create a patterned orientation for an LCP
material. Preferably, the alignment layer is a photo-alignment
layer, which preferably has been aligned by the method of the
invention.
First and second directions of light for which the device of FIG. 4
works, are defined by the geometry of the POE as well as by the
pattern in the polarizing layer. In the example of FIG. 4, the
polarizing layer is not positioned in the focal plane of the
lenticular lenses, which has the consequence that collimated light
47 and 50 is directed to the full width of stripes 43 and 45. If
the pattern in the polarizing layer has been generated by a method
according to the invention, wherein a photo-alignment layer was
already attached to the lenticular lens array during irradiation
with aligning light, then each type of stripes could have been
created by a single irradiation with collimated light. The
incidence angle dependent polarizer shown in FIG. 4, works only
well for a small range of incidence angles. For other incidence
angles, the areas on the polarizing layer to which the light is
redirected do not fully coincide with the regions 43 or 45 anymore,
so that the polarization degree of the transmitted light decreases.
FIG. 5 shows a similar device 60 with a POE 62 having a lenticular
lens array and in combination a polarizing layer 61 with regions 63
and 65 having polarization directions 64 and 66, respectively. The
difference to FIG. 4 is that the regions with different
polarization directions are broader and the polarizing layer is
closer to the focal plane of the lenticular lenses. As a
consequence, collimated incident light is redirected by the POE
only to a small area of the stripes 63 and 65, respectively. For
example, the non-polarized light 67 in FIG. 5a, incident under a
first angle is redirected to a small area on the left of region 63,
which causes the transmitted light 68 to be polarized with a
polarization direction 69. Non-polarized light 70 in FIG. 5b,
incident under a second angle is redirected to a small area on the
right of region 63, which causes the transmitted light 71 also to
be polarized with the polarization direction 69. The situation is
similar for light incident from opposite directions, which will be
redirected to regions 65 with another polarization direction 66.
Hence the device 60 of FIG. 5 has a much broader range of incidence
angles for which it works properly.
A device according to FIG. 5 can be manufactured using a method of
the invention, by generating an orientation pattern in a
photo-alignment layer which then, for example, transfers the
orientation pattern to an LCP layer comprising dichroic dyes. The
photo-alignment layer may be already attached to the POE during
irradiation with aligning light. Because the focusing behavior of
the lenticular lenses during irradiation of the photo-alignment
layer is almost the same as it is in the final polarizing device
60, a single irradiation with collimated light would not be
sufficient to generate the full width of the regions 63 and 65,
respectively. Therefore, the irradiation of the photo-alignment
layer during production may either employ multiple irradiation
steps with aligning light incident under different angles or may
use a single irradiation step with non-collimated aligning light,
which provides a sufficient range of incidence angles.
The assumed polarization directions in the polarizing layers 41, 61
of FIGS. 4 and 5 are examples only and shall not be interpreted as
a limitation. It is even possible to incorporate a multitude of
regions with different polarization directions in a device
described above. The number of possible polarization directions
that can be selected by adjusting the angle of light incidence is
determined by the number of regions with different polarization
directions. The angle of incidence to be selected for a certain
polarization direction depends on the geometry of both the pattern
and the POE.
As is clear from the description and the related figures, a
polarizing device as described above also works for light which
enters the device from the polarizing layer side. Further, such a
device can also be used as an analyzer, for example to analyze the
polarization direction of linearly polarized light.
Contrary to standard sheet polarizers, which, for example, have to
be rotated by 90.degree. to change from parallel to perpendicular
polarization, a device according to the invention has only to be
tilted to achieve the same, provided that regions with 0.degree.
and 90.degree. polarization directions are available. Applications
are, therefore, preferably those in which different polarization
directions are desired, but rotation of a polarizer is restricted.
For example, there are optical elements, in particular in the field
of optical security elements, which comprise orientation patterned
optical retarders and which when analyzed with a properly oriented
standard sheet polarizer, show an image with positive contrast and
which show the negative of the image upon rotating the polarizer by
45.degree.. Such elements are similar to those disclosed in U.S.
Pat. No. 7,375,888, already referred to in the introductory part of
this application. Because not everybody has a sheet polarizer at
hand for verifying such security elements, it would be advantageous
to provide the polarizer together with the security element. This
could be done, for example, by arranging the security element and
the polarizer on the same substrate, for example a banknote, such
that by folding the substrate, the polarizer can be used to analyze
the security element. Another way to provide the polarizer together
with the optical security element is to arrange the security
element and the polarizer on two separate pages of a booklet, for
example in a passport, such that the security element can be
analyzed by turning the corresponding page in order to bring the
polarizer in front of the security element. Transparent windows may
be used to improve the visibility of the image to be observed. The
drawback of the above applications is that the polarizer may hardly
be rotated against the security element and hence the contrast
inverted image cannot be observed. However, if in the above
application examples a polarizing device according to the first
preferred embodiment is used instead of a standard polarizing
sheet, then upon arranging polarizer and optical element above each
other, the hidden image stored in the security element can be made
visible as positive and as negative image just by changing the
angle of view or by tilting the substrate or booklet, respectively.
FIG. 6 shows an example of a booklet 80 with a hidden image stored
in a patterned retarder 81 on a first page 82 and in a transparent
window on a second page 84 a device 83 according to the first
preferred embodiment. The device preferably has two types of
polarizing regions, which differ in the direction of polarization
by 45.degree.. As long as page 84 is not turned to cover page 82,
the image stored in the element 81 is not visible. After turning
page 84, the polarizing device 83 overlaps with the element 81 and
the image stored in element 81 can be seen, for example, with a
positive contrast when viewed from a first position 85 and with a
negative contrast when viewed from a second position 86.
A second preferred embodiment of a device according to the
invention is an optically retarding device, which provides
different optical axes directions for light incident from different
directions. Any type of POE can be used for such a device as long
as it does not substantially change the polarization state of the
light. The optical element is a patterned retarder layer with
regions of different directions of the optical axes. As an example,
FIG. 7 shows cross-sections through a device 90 comprising a POE 92
with a parallax barrier plate on top. If the POE comprises a
dielectric material, such as glass or plastic, the refractive index
of the dielectric material causes a change of the light path
direction inside the POE, as indicated in the drawings of FIG. 7.
The parallax barrier plate comprises transparent sections 93 and
opaque sections 94, preferably in the form of stripes, which means
that sections 93 and 94 extend along the direction perpendicular to
the drawing plane. The device further comprises a retarder layer 91
with regions 95, 97 of different optical axes directions 96, 98.
Preferably, the regions are formed as stripes. For the example in
FIG. 7 it is assumed that the retarder layer acts as a quarter wave
retarder for the incident angle the device is designed for. Light
may be incident from the POE side or from the retarder layer side.
In FIG. 7a it is assumed that linearly polarized light 99 is
incident from a first direction onto the retarder layer 91 and that
the polarization direction 100 lies in the drawing plane. It is
further assumed that the optical axes of the retarder layer are not
tilted with regard to the layer plane and that the directions 96,
98 are perpendicular to each other and oriented at an angle of
45.degree. to the polarization plane of the incident light 99.
Because the incident direction for light 99 is chosen such that
light transmitted through regions 97 is blocked by the opaque
sections 94 of the barrier plate, only light 101 is transmitted
through the device, which has passed regions 95. The quarter wave
property of the retarder layer 91 converts linearly polarized light
into circularly polarized light of a first handedness 102, for
example it may be left handed. FIG. 7b illustrates the situation
where light 103 with a polarization direction 104, which lies
within the same polarization plane as in FIG. 7a, is incident to
the retarder layer from a second direction, such that light which
passes regions 95 are blocked by the opaque sections 94 of the
barrier plate. Accordingly, only light, which has passed regions 97
of the retarder layer is transmitted through device 90. Because
regions 97 also act as a quarter wave retarder, the transmitted
light 105 is again circularly polarized, but since the polarization
direction 98 in region 97 is perpendicular to the polarization
direction 96 in region 95, the handedness is opposite to that of
light 101 of FIG. 7a, for example it is right handed circularly
polarized. Hence, the device 90 converts linearly polarized light
into left handed or right handed circularly polarized, depending on
the incidence angle. For light incident from other directions than
99 and 103, both types of regions 95 and 97 contribute to the
transmitted light, which in general will be elliptically polarized.
Thus it is possible to tune the ellipticity of the transmitted
light by changing the angle of incidence.
If both the light 99 and 103 is either left- or right handed
circularly polarized, then the light 101 and 105, which is
transmitted through device 90 is linearly polarized, with a
polarization direction parallel and perpendicular to the drawing
plane, respectively.
FIG. 7 is only a specific variant of the second preferred
embodiment. As mentioned already above, other types of POEs could
alternatively be used, such as a lenticular lens array. Further,
for the retarder layer 91 any other value than a quarter wave may
be used as a retardance; the number of regions with different
optical axes directions may be different from two and any direction
of the optical axis is possible. Another special case would be a
device with a retarder layer that acts as a half wave plate. If for
this case it is assumed that the optical axis direction 96 in
region 95 is within the polarization plane of the incident linearly
polarized light 99, whereas the optical axes direction 98 differs
from direction 96 by an angle of 45.degree., then the device 90 in
FIG. 7a would not affect the polarization state of incident light
99 in the effective areas and the light transmitted through device
90 would be linearly polarized with same direction 100. For
polarized light incident from a second direction 103, corresponding
to FIG. 7b, the linearly polarized light will be rotated by
90.degree. upon transmitting the quarter wave retarder in regions
97, such that the polarization direction is perpendicular to the
drawing plane of FIG. 7b. For this example, light incident from the
two directions is transmitted as linearly polarized light, either
polarized parallel or perpendicular to a reference plane. The
person skilled in the art will appreciate that the number of
regions with different optical axis directions may be different
from two and that the optical axes directions may differ by any
value, rather than only by 45.degree..
Preferably, a device of the second preferred embodiment comprises
an additional patterned- or non-patterned polarizing layer, for
example adjacent to the patterned retarder layer. The device can
then, for example, be used as an angle dependent polarizer or
analyzer.
Like for devices according to the first preferred embodiment, the
devices of the second preferred embodiment may be applied for
analyzing polarization states of light, for example by tilting the
device or by changing the angle of view. In particular such devices
are useful for visual observation of security elements which
modulate the polarization state of light, such as the elements
incorporating orientation patterned retarders.
A third preferred embodiment of a device according to the invention
comprises a POE and an orientation patterned retarder layer, like
in case of the second preferred embodiment. However, the
orientation pattern differs from that of the second preferred
embodiment, in that the different regions, which are optically
effective for light of certain incidence angles, do not have a
uniform orientation of the optical axes. Rather than that, the
regions comprise zones, which differ by the directions of the
optical axis. The optical axis direction of each zone can, for
example, encode part of an information. The number of different
optical axis directions is not limited. It is even possible that
the optical axes direction changes continuously. In the context of
this application an area comprising a continuous variation of
optical axes directions shall be interpreted as a number of
neighboring zones, wherein a zone is defined as a small area with
almost uniform orientation of the optical axis. The information
may, for example, be represented by the zones of all regions that
are optically effective for a certain light incidence or
observation angle. In this way, it is possible to store second and
further information in second and further sets of regions, which
can be selected by second and further incidence or observation
angles, respectively. However, neither first, nor second
information is visible in normal environmental lighting conditions,
where the light is non-polarized. Even if the device is illuminated
with polarized light, the information cannot be seen, since the
information is only encoded by the optical axes of a birefringent
layer, which causes a spatial modulation of the polarization state
of light, for which the human is, however, not sensitive. The
information stored in the device becomes only visible if the device
is illuminated with polarized light and the transmitted light is
observed through a linear or circular polarizer. Upon illumination
with polarized light and with an analyzer in a proper position, the
different information can be seen one after the other by changing
the angle of observation or by tilting the device. A device
according to the third preferred embodiment is, therefore,
preferably used as an optical security device.
The angular range under which one information is visible depends on
the geometry of the POE and of the pattern. For example, it is
possible to enhance the viewing range for each of the information,
by storing the same image for a number of incidence angles. In an
extreme case, a first information is visible when looking to the
device, for example, from the left side and a second information is
visible when looking to the device from the right side. It is also
possible to design the device such that both eyes of an observer
see a different image, for example, two images which are combined
in the human brain as a 3D-image.
Preferably a security device according to the invention is combined
with other security features. In a simple case, the device may be
combined with permanently visible information, preferably also
different for different viewing angles. Without an analyzer only
the permanent information is visible, whereas when observed with an
analyzer, both the encoded and the permanently visible information
can be seen in combination. As an example, the information encoded
in the retarder layer may provide the respective parts of a
3D-image to left and right eye of an observer. Without an analyzer
only the permanent information is visible. Upon arranging an
analyzer in a proper position, a 3D-image appears, for example, at
a distance above the permanently visible image.
Preferably, a device according to the third preferred embodiment is
permanently combined with a polarizing sheet or layer in order to
provide polarization means for incident non-polarized light.
The fourth preferred embodiment of a device according to the
invention is similar to the third preferred embodiment in terms of
storing information, but uses a patterned polarizing layer, as in
the first preferred embodiment instead of a retarder layer. Similar
to the third preferred embodiment, different information can be
stored for different observation angles by encoding the respective
information in zones of different polarization directions. While
the encoding of information for different viewing angles and the
application as security device is similar to that described for the
third preferred embodiment, the way of analyzing a device according
to the fourth preferred embodiment is slightly different. The
difference is mainly related to the fact that the patterned
anisotropic layer acts as a polarizer and therefore does not
require both incident polarized light and an analyzer, but only one
of them. For example, if the incident light is polarized, then the
patterned polarizer of the device acts as an analyzer and controls
local transmittance depending on the angle between the local
polarization axis of the device and the polarization plane of the
incident polarized light. On the other hand, if the incident light
is non-polarized, then the light transmitted through the device is
polarized and has a spatial modulation of the polarization
direction. By using an analyzer the spatial modulation of the light
is converted in a spatial brightness modulation, thus decoding the
information, which becomes visible for an observer or detectable by
a machine, respectively.
The fifth preferred embodiment of a device according to the
invention is similar to the third and fourth preferred embodiment
in terms of storing information, however, the patterned optical
element comprises anisotropically absorbing and/or emitting
fluorescent dyes, wherein the direction of maximum absorption
and/or emission is different in different zones of the pattern. The
direction of maximum absorption shall mean the direction in the
layer plane, for which the absorption of light is maximum. The
direction of maximum emission corresponds to the polarization
direction of the emitted light. Similar to the third and fourth
preferred embodiments, different information can be stored for
different observation angles by encoding the respective information
in zones of different anisotropy directions. Encoding of
information for different viewing angles and the application as
security device is similar to that described for the third and
fourth preferred embodiments. For many applications it is preferred
that there are at least two zones, for which the directions of
maximum absorption and/or emission, respectively, differs by about
90.degree.. In this case, the zones can be distinguished with
maximum contrast. However, any other angle than 90.degree. is
possible, for example, to encode grey levels. Preferably, the
optical element comprises a layer of patterned LCP, in which
fluorescent molecules are embedded. If the fluorescent molecules
absorb the exciting light anisotropically, then incident linearly
polarized light of suitable polarization direction may be used for
observation, which has the effect that those zones, which have a
smaller angle between absorption and polarization direction absorb
more light. On the other hand, zones in which the absorption axis
is perpendicular to the polarization direction of the incident
light have the lowest absorption. Because the intensity of the
fluorescent light is higher the more exciting light is absorbed,
the differently oriented zones fluoresce with different
intensities. Thus, the information is visible for an observer
without an analyzer. If the fluorescent molecules emit light
anisotropically, which means the light is polarized, then it may be
possible to illuminate the differently oriented zones with
non-polarized exciting light, upon which the differently oriented
zones fluoresce with different polarization directions, such that
the stored information can be decoded by a linear polarizer.
If in the devices according to the invention a parallax barrier
plate is used as a POE, the light blocking sections may also be
reflective, in particular at the side towards the anisotropic
optical element. In this case, the POE can be operated both in
transmissive and in reflective mode. In transmissive mode, the
light transmitted through the transmissive sections is the desired
light and the device works as described for the preferred
embodiments above. When operated in reflective mode, the light
reflected at the reflective light blocking sections is the desired
light, whereas the light transmitted through the transmissive
sections may no longer be considered.
In case of devices according to the invention which are operated in
reflective mode the observing light enters the device through the
anisotropic element, which it passes a second time after being
reflected at the reflective barrier. If the optical element is
based on birefringent properties, which requires polarized light
for observation, the parallax between the paths of the incoming and
reflected light may cause interference between different zones of
the optical element. This can be avoided if the reflective light
blocking sections are either covered by a polarizer or comprise
reflective polarizers. The incident light may then be non-polarized
and will not interact with the birefringent material until it is
polarized at the reflective sections of the barrier plate.
Accordingly, only the reflected light will be polarized and can
interact with the desired zones of the birefringent optical
element.
In principle, the devices of the invention work for a large range
of thicknesses. However, there are certain applications, which do
not tolerate devices which exceed a certain thickness. Because
parallax optical elements need a certain distance to generate the
desired parallax, the POEs have to be especially designed for such
applications. Preferably, the thickness of a device according to
the invention is less than 100 .mu.m, more preferred less than 60
.mu.m and most preferred less than 30 .mu.m.
If a parallax plate is used as a POE, it should have a proper
distance from the element with patterned optical properties in
order to provide a sufficient parallax effect in a reasonable range
of viewing angles. The proper distance depends on the width of the
light transmissive and light blocking sections of the parallax
plate. If the space between the parallax plate and the element with
patterned optical property is filled with air, then the distance
between the parallax plate and the optical element is preferably
larger than 0.2 times the width of a light transmissive section of
the parallax plate. More preferred is that the distance is larger
than 0.4 times the width of a light transmissive section and most
preferred larger than 0.6 times the width of a light transmissive
section of the parallax plate. However, if there is a dielectric
material between the parallax plate and the optical element, such
as glass or plastic, then the distance between the parallax plate
and the optical element is preferably larger than 0.5 times the
width of a light transmissive section of the parallax plate. More
preferred is that the distance is larger than 0.8 times the width
of a light transmissive section and most preferred larger than one
time the width of a light transmissive section of the parallax
plate.
A device according to the invention may be used in combination with
other optical devices. In particular, if the optical element with
patterned optical property is an optically retarding device, the
pattern is not visible in normal, non-polarized light. Therefore,
the POE of the device according the invention may be used for
observation of another device without being disturbed by the
pattern. The other device may, for example, also have a pattern,
which in combination with the POE of the device of the present
invention generates certain optical effects. The resulting effect
may also be viewing angle dependent or may be a Moire effect. The
device according to the invention and the other device may be
arranged on the same substrate, such as a banknote, so that by
folding the substrate the two devices can easily be arranged above
each other for the time of observation.
In any of the embodiments above, the orientation directions, which
have been assumed as examples, shall not limit the scope of the
invention. In principle, any other direction is possible, as long
as not explicitly excluded.
A photo-alignable material in a photo-alignment layer for any of
the methods and devices described above may be any kind of
photo-sensitive material in which anisotropic properties can be
created upon exposure to aligning light, independent from the
photo-reaction mechanism. Therefore, suitable photo-alignable
materials are, for example, materials in which upon exposure to
aligning light the anisotropy is induced by photo-dimerization,
photo-decomposition, trans-cis isomerization or photo-fries
rearrangement. Preferred photo-alignable materials are those, in
which upon exposure to aligning light the created anisotropy is
such that slave materials in contact with the photo-aligned
material can be oriented. Preferably, such slave material is a
liquid crystal material, in particular a LCP-material.
Photo-alignable materials, as those described above, incorporate
photo-alignable moieties, which are capable of developing a
preferred direction upon exposure to aligning light and thus
creating anisotropic properties. Such photo-alignable moieties
preferably have anisotropic absorption properties. Typically, such
moieties exhibit absorption within the wavelength range from 230 to
500 nm. Preferably, the photo-alignable moieties exhibit absorption
of light in the wavelength range from 300 to 450 nm, more preferred
are moieties, which exhibit absorption in the wavelength range from
350 to 420 nm.
Preferably the photo-alignable moieties have carbon-carbon,
carbon-nitrogen, or nitrogen-nitrogen double bonds.
For example, photo-alignable moieties are substituted or
un-substituted azo dyes, anthraquinone, coumarin, mericyanine,
2-phenylazothiazole, 2-phenylazo-benzthiazole, stilbene,
cyanostilbene, fluorostilbene, cinnamonitrile, chalcone, cinnamate,
cyanocinnamate, stilbazolium, 1,4-bis(2-phenylethylenyl)benzene,
4,4'-bis(arylazo)stilbenes, perylene,
4,8-diamino-1,5-naphthoquinone dyes, aryloxy-carboxylic
derivatives, arylester, N-arylamide, polyimide, diaryl ketones,
having a ketone moiety or ketone derivative in conjugation with two
aromatic rings, such as for example substituted benzophenones,
benzophenone imines, phenylhydrazones, and semicarbazones.
Preparation of the anisotropically absorbing materials listed above
are well known as shown, e.g. by Hoffman et al., U.S. Pat. No.
4,565,424, Jones et al., in U.S. Pat. No. 4,401,369, Cole, Jr. et
al., in U.S. Pat. No. 4,122,027, Etzbach et al., in U.S. Pat. No.
4,667,020, and Shannon et al., in U.S. Pat. No. 5,389,285.
Preferably, the photo-alignable moieties comprise arylazo,
poly(arylazo), stilbene, cyanostilbene, cinnamate or chalcone.
A photo-alignable material may have the form of a monomer, oligomer
or polymer. The photo-alignable moieties can be covalently bonded
within the main chain or within a side chain of a polymer or
oligomer or they may be part of a monomer. A photo-alignable
material may further be a copolymer comprising different types of
photo-alignable moieties or it may be a copolymer comprising side
chains with and without photo-alignable moieties.
Polymers denotes for example to polyacrylate, polymethacrylate,
polyimide, polyamic acids, polymaleinimide, poly-2-chloroacrylate,
poly-2-phenylacrylate; unsubstituted or with C.sub.1-C.sub.6 alkyl
substituted poylacrylamide, polymethacyrlamide,
poly-2-chloroacrylamide, poly-2-phenylacrylamide, polyether,
polyvinylether, polyester, polyvinylester, polystyrene-derivatives,
polysiloxane, straight-chain or branched alkyl esters of
polyacrylic or polymethacrylic acids; polyphenoxyalkylacrylates,
polyphenoxyalkylmethacrylates, polyphenylalkylmethacrylates, with
alkyl residues of 1-20 carbon atoms; polyacrylnitril,
polymethacrylnitril, cycloolephinic polymers, polystyrene,
poly-4-methylstyrene or mixtures thereof.
A photo-alignable material may also comprise photo-sensitizers, for
example, ketocoumarines and benzophenones.
Further, preferred photo-alignable monomers or oligomers or
polymers are described in U.S. Pat. Nos. 5,539,074, 6,201,087,
6,107,427, 6,632,909 and 7,959,990.
It should be understood that the intention is not to limit the
invention to particular embodiments described. On the contrary, the
intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
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